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At least 271 records · Page 15Linked to original sources
PubMed2006

[The influence of heat/pressure polymerization method on the adaptation of complete denture base].

PURPOSE: The purpose of this in vitro study is to investigate the mechanical ability and adaptation of complete denture base by the use of thermoformed resin cured with heat/pressure injection method. METHODS: The flexural strength, the surface hardness and the adaptation of thermoformed resin and SR Ivoclar capsule resin were compared between using the conventional water bath-cured method and heat/pressure injection method. The collected date were analyzed statistically using the two-sample t test at alpha=0.05. RESULTS: The thermoformed resin cured with heat/pressure injection method has significant difference from that cured with conventional water bath-cured method on flexural strength and surface hardness (P<0.05). The upper partial base had significant difference in the gap distance at point A, B, D and E (P<0.05) between the thermoformed denture base cured with heat/pressure injection method and conventional water bath-cured method. CONCLUSIONS: These findings indicate that the thermoformed resin cured with heat/pressure injection method has better mechanical abilities and adaptation than that cured with conventional water bath-cured method.

Acrylic Resins↗
PubMed1997

Lased and sandblasted denture base surface preparations affecting resilient liner bonding.

STATEMENT OF PROBLEM: Adhesive failure between the liner and the denture base creates an environment for potential bacterial growth and accelerated breakdown of the soft liner resulting in a deteriorating prosthesis. PURPOSE: This study evaluated the effects of a specific sandblasted or lased preparation on the interfacial bonding of polymethyl methacrylate and silicone and polyethyl methacrylate resilient liners. MATERIAL AND METHODS: Polymethyl methacrylate test specimens were fabricated and received one of three surface treatments: untreated (control), sandblasted (250 microns aluminum oxide particles), and lased (carbon dioxide). Polyethyl methacrylate and silicone resilient lining materials were applied to these surfaces and the peel strengths were determined with the American Society for Testing and Materials peelin-adhesion test. RESULTS: Altering the polymethyl methacrylate surface by sandblasting significantly reduced the peel strengths for the polymethyl methacrylate/polyethyl methacrylate and polymethyl methacrylate/silicone specimens. Altering the polymethyl methacrylate surface by delivering carbon dioxide laser energy to form a grid pattern produced lower peel strengths that were statistically significant from the controls for the polymethyl methacrylate/polyethyl methacrylate specimens, but not so for the polymethyl methacrylate/silicone specimens. Untreated polymethyl methacrylate/polyethyl methacrylate peel strengths were significantly higher than polymethyl methacrylate/silicone. CONCLUSIONS: Results of this study imply that mechanical surface preparation of denture bases before application of a resilient liner may not be warranted.

Adhesiveness↗
PubMed2005

Electron beam irradiation of denture base materials.

UNLABELLED: Electron beam irradiation can be used to influence the properties of polymers. It was the aim of this study to investigate whether PMMA denture base materials can benefit from irradiation in order to have increased fracture toughness, work of fracture or hardness. Rectangular specimens of heat-and auto-curing denture base materials were electron beam irradiated (post-cured) with 25, 100 and 200 kGy using an electron acceleration of 10 MeV or 4.5 MeV respectively. Fracture toughness, work of fracture, Vickers hardness and colour changes were measured and compared with not-irradiated specimens. The toughness, work of fracture and hardness increased using 10 MeV with a dose of 25 kGy and with 100 kGy using 4.5 MeV. However, the clinical use may not benefit from the observed small changes. Higher dosage (200 kGy) decreased the values significantly. The colour changes reached a level which was found to be not clinically acceptable. CONCLUSION: PMMA denture base materials do not benefit from post-curing with electron beam irradiation.

Dental Materials↗
PubMed1994

Repair of denture base resins using visible light-cured materials.

Specimens of denture base resins were repaired with autopolymerizing and visible light-cured (VLC) repair materials. Flexural properties were measured and revealed that the highest strength and toughness of joint are obtained by the autopolymerizing repair material and are independent on the base resin. The VLC materials exhibited a lower repair strength (22% to 58%) and toughness (9% to 33%) than those of the autopolymerizing resin. No interaction between base and repair material was detected, which was attributed to poor adhesive bonding created at the interface.

Acrylic Resins↗
PubMed1989

[Acrylic materials for denture bases in dentistry. Study of measurement variations and the influence of three new parameters on construction of bases and their deformation].

A further study of the variance of deviation measurements of denture bases in the palate region shows that the variability of measurements is not essentially due to measuring, but also to the variability of denture processing. No more than the other previously studied parameters, the heating and cooling rates as well as the mode of insertion of resin in the cast have no effect on the dimensional accuracy of denture bases after curing.

Acrylic Resins↗
PubMed1993

Impact strength of acrylic resin denture base materials with surface defects.

The first part of this study involved the development of a method for evaluating the effect of small surface defects (3.0 microns-80.0 microns) on the impact strength of acrylic denture base materials. The method was used to compare the properties of 12 denture base materials, some of which are described as "high-impact strength" products. The defects were introduced by drawing the specimens over abrasive papers of varying grit sizes or by notching with a craft knife. Flexural toughness tests were also carried out in order to evaluate the materials under both rapid (impact) and slow (flexural) rate test conditions. The impact resistance of acrylic resins was significantly reduced by the presence of very small surface defects (e.g., < 16 microns), and this was particularly noticeable for so-called high-impact resins. The latter have values of impact strength only slightly higher than standard acrylic products when defects are present. Testing "notched" specimens with small surface defects was a simple method of obtaining reproducible results. This test was sensitive enough to differentiate among several types of currently available denture base resins.

Acrylic Resins↗
PubMed2006

In vitro adhesion of Candida species to denture base materials.

Adhesion of Candida species to prosthetic acrylic resins is an essential first step in the pathogenesis of denture stomatitis. Data on the relative adhesion of pathogenic non-albicans Candida species to different denture base materials are sparse. The purpose of the present study was to investigate in vitro adhesion of C. albicans, C. glabrata, C. krusei and C. dubliniensis to four different denture base materials. Specimens of both heat-cured resins (Vertex(TM) Rapid Simplified and ProBase Hot) and cold-cured resins (Paladur A and Paladur B) were prepared using a novel method and the adhesion of four strains each of the foregoing Candida species evaluated microscopically using a soft imaging system. There was a significant difference in yeast adherence between Vertex and the other resins. Only C. glabrata attached to Vertex, while all the remainder of the tested species adhered to all other resins tested except ProBase, which resisted C. krusei adhesion. There was a significant difference in candidal adhesion between cold-cured and heat-cured resins for three Candida species (C. albicans, P = 0.039; C. glabrata, P = 0.002 and C. krusei, P = 0.000). The type of denture base material and whether they are heat-cured or cold-cured play an important role in modifying candidal adhesion.

Acrylic Resins↗
PubMed1998

Distortion behavior of heat-activated acrylic denture-base resin in conventional and long, low-temperature processing methods.

There have been many reports on fatal distortion of heat-activated acrylic denture-base resin which is still widely used in the field of removable prosthodontics. However, these reports have failed to report quantitatively on polymerization and thermal shrinkage factors. In the present study, we attempted to verify that the shrinkage of heat-activated acrylic denture-base resin was caused mainly by thermal contraction after processing. Furthermore, we examined the degree of distortion resulting from long, low-temperature processing, and compared the results with that of the conventional method. The strain gauge and thermo-couple were embedded in a specimen at the time of resin packing. The measurement started from the beginning of processing and continued until the specimen was bench-cooled and immediately before and after it was de-flasked, as well as during seven-day immersion in water at 37 degrees C. The resin expanded when processed by the conventional method. Meanwhile, mild shrinkage, possibly polymerization shrinkage, was observed when the resin was processed by the low-temperature method. This suggested that polymerization shrinkage was compensated for by thermal expansion during processing by the conventional method. Moreover, the shrinkage strains in the period from the completion of processing to immediately after de-flasking, in both the conventional and low-temperature methods, were identical to the theoretical value of thermal shrinkage which we obtained by multiplying the linear coefficients of thermal expansion by temperature differences. The shrinkage strain in the specimen processed by the low-temperature method, measured from the end of processing to immediately after de-flasking, averaged 64% of that in the specimen processed by the conventional method. The results revealed quantitatively that the shrinkage of heat-activated acrylic denture-base resin was mainly thermal shrinkage, and demonstrated the advantage of the low-temperature method in reducing thermal shrinkage.

Acrylic Resins↗
PubMedDate not supplied

Microwave energy polymerization of poly(methyl methacrylate) denture base resin.

Several physical property tests were conducted to compare microwave energy and conventional hot water bath polymerization techniques. The two methods of polymerization produced similar dimensional accuracy in complete denture bases. No differences were found in transverse strength, Knoop hardness, density, and residual monomer content of resin test strips. Comparable strength was found between microwave-polymerized and autopolymerized repairs of resin test strips. No porosity was observed in complete or removable partial denture bases polymerized by either technique. The Knoop hardness of microwave-polymerized removable partial denture bases was found to be slightly lower near the metal framework.

Denture Bases↗
PubMed2001

Bonding strength between a hard chairside reline resin and a denture base material as influenced by surface treatment.

Direct relining of dentures made with hard chairside reline resins is faster than laboratory-processed reline systems and the patient is not without the prosthesis for the time necessary to perform the laboratory procedures. However, a weak bond between the autopolymerizing acrylic reline resins and the denture base material has been observed. This study evaluated the effect of six different surface treatments on the bond strength between a hard chairside reline acrylic resin and a heat-cured acrylic resin. Specimens of the heat-cured acrylic resin were divided into seven groups. One of these groups remained intact. In the other groups, a 10-mm square section was removed from the centre of each specimen. The bonding surfaces were then treated with (i) methyl methacrylate monomer, (ii) isobutyl methacrylate monomer, (iii) chloroform, (iv) acetone, (v) experimental adhesive and (vi) no surface treatment -- control group. Kooliner acrylic resin was packed into the square sections and polymerized. The bonding strength was evaluated by a three-point loading test. The results were submitted to one-way analysis of variance (ANOVA) followed by a Tukey multiple range test at a 5% level of significance. No significant difference was found between the surface treatment with Lucitone 550 monomer or chloroform, but both were stronger than the majority of the other groups. The bond strength provided by all the surface treatments was lower than that of the intact heat-cured resin.

Acetone↗
PubMed1980

Release of formaldehyde from denture base polymers.

The release of formaldehyde in an aqueous environment at 37 degrees C from the surface of heat-polymerized, and auto-polymerized dough and pour type acrylic denture base materials was determined quantitatively. The analytical method used was based on determination of the reaction product of formaldehyde and dimedone by means of high performance liquid chromatography (HPLC), i.e. the method is spesific for formaldehyde. Chemical model reactions were carried out to simulate possible reaction mechanisms for the formation of formaldehyde in denture base polymers. The quantities of released formaldehyde was dependent on the processing conditions and composition of the material. Heat-polymerized denture base materials released considerably less formaldehyde than the auto-polymerized dough and pour types of materials.

Acrylic Resins↗
PubMed1990

[Development of internal stresses in denture bases during the procedures of curing, finishing and polishing].

The development of internal stresses in denture bases, during the procedures of curing, finishing and polishing is a very important factor and the power of these stresses is often of a remarkable level. In this article there are described the cases in which stresses are possible to develop inside the denture bases during the various processes of curing, finishing and polishing of the dentures as well the methods which are used to reduce their results on the finished dentures.

Acrylic Resins↗
PubMedDate not supplied

Water sorption and dimensional changes of denture base polymer reinforced with glass fibers in continuous unidirectional and woven form.

PURPOSE: The aim of this study was to determine the dimensional accuracy and water sorption of a denture base polymer that was reinforced with glass fibers in continuous unidirectional and woven form in different weight fractions. MATERIALS AND METHODS: Ten rhombic brass plates were prepared with reference points, and 70 heat-cured denture base polymer specimens were produced using these brass models. Ten of 70 were used for controls, and 60 were reinforced with glass fibers in continuous parallel and woven form. The dimensional changes of polymer and fiber-reinforced composite specimens after processing, drying for 4 days at 37 degrees C, and storage in 37 degrees C water for 90 days were calculated by the change of the distance vector. The measurements were made between the reference points on the specimens and were compared with those on the brass model at 4 different stages. The water sorption calculations were made at 10 different time intervals on 70 specimens, which were immersed in a 37 degrees C distilled water bath and weighed. RESULTS: The polymerization shrinkage and water sorption of denture base polymers is lower when the specimens are reinforced with glass fibers in continuous unidirectional and woven form. The highest fiber content showed the smallest dimensional change (0.069 mm, or 0.25%), and the unreinforced group showed the largest change (0.139 mm, or 0.54%). Water sorption occurred mainly during the first 14 days. CONCLUSION: As the fiber content increases, the dimensional change and water sorption decrease.

Absorption↗
PubMed1990

Effect of cross-linking on sorption properties of a denture-base material.

Cross-linking of the polymer of the interstitial matrix of a heat-cured resin denture base is said to provide craze resistance for the denture base. The mechanism of crazing can be related to both water sorption and solvent attack. The present study shows that the addition of ethylene glycol dimethacrylate in concentrations of 0-100% of monomer volume has little effect on water sorption properties but is an efficient method of providing solvent resistance.

Cross-Linking Reagents↗
PubMed1992

The transverse strengths of three denture base resins reinforced with polyethylene fibers.

This investigation compared the transverse strengths of three denture base resins with and without polyethylene reinforcement fibers. These fibers were incorporated in 10 specimens each of a high-impact strength resin, a rapid heat-polymerized resin, and a light-activated resin. Each specimen was broken on an Instron universal testing machine using a three-point load after processing and air drying. The values obtained were then compared with values previously recorded for the same type of specimens without incorporated fibers. Only the light-activated denture base resin specimens exhibited a significantly higher mean transverse strength after polyethylene fiber reinforcement.

Acrylic Resins↗
PubMed2005

Use of a light-polymerized composite removable partial denture base for a patient hypersensitive to poly(methyl methacrylate), polysulfone, and polycarbonate: a clinical report.

This article describes a light-polymerized composite denture base used for a patient with hypersensitivity to poly(methyl methacrylate) (PMMA), polysulfone (PSF), and polycarbonate (PC). A urethane-dimethacrylate (UDMA) composite was used as an alternative to fabricate both the denture base and the custom artificial teeth. Immediately after placing the new prosthesis, allergic symptoms disappeared from the patient's mucous membrane. The denture has functioned satisfactorily for more than 2.5 years without recurrence of the hypersensitivity.

Acrylic Resins↗